Increasingly stringent statutory regulations regarding allowable emissions of noxious substances from motor vehicles, in which internal combustion engines are disposed, make it necessary to keep emissions of noxious substances during operation of the internal combustion engine as low as possible. This may be done, on the one hand, by reducing the emissions of noxious substances that arise during burning of the air-fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, for internal combustion engines exhaust treatment systems are used, by means of which the emissions of noxious substances generated during the process of burning the air-fuel mixture in the respective cylinders are converted into harmless substances. For this purpose catalytic converters are used, which convert carbon monoxide, hydrocarbons and nitrous oxides into harmless substances. Both purposeful influencing of the production of noxious substance emissions during combustion and highly efficient conversion of the noxious components by means of a catalytic converter presuppose a very precisely adjusted air-fuel mixture in the respective cylinder.
From the textbook “Internal Combustion Engine Manual”, published by Richard von Basshuysen, Fred Schafer, second edition, Vieweg & Sohn Verlaggesellschaft mbH, June 2002, pp. 559 to 561, a linear lambda controller is known, comprising a linear lambda probe, which is disposed upstream of a catalytic converter, and a binary lambda probe, which is disposed downstream of the catalytic converter. A lambda setpoint value is filtered by means of a filter that takes into account delays in exhaust gas analysis and the sensor response. The lambda setpoint value thus filtered is the controlled variable of a PI2D lambda controller, the manipulated variable of which is an injection quantity correction.
Furthermore, from the same pages of the same textbook a binary lambda controller is also known, comprising a binary lambda probe, which is disposed upstream of the catalytic converter. The binary lambda controller comprises a PI controller, the P- and I components being stored in engine speed- and load characteristic maps. In the case of the binary lambda controller, the excitation of the catalytic converter, also described as lambda fluctuation, arises implicitly as a result of the two-step control. The amplitude of the lambda fluctuation is set to approximately 3%.
DE 19702556 A1 discloses a device for detecting the fuel properties for an internal combustion engine, which device detects the property of the fuel used by the engine from the operating state during the start of the engine and emits a signal that indicates the detected fuel property. The property of the fuel used is determined on the basis of a parameter representing the starting performance of the internal combustion engine and a parameter representing the revolution change during the start.
The underlying object of the invention is to provide a method and a device for operating an internal combustion engine, which are simple and also precise.
The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims.
An embodiment of the invention is notable for a method and a device for operating an internal combustion engine comprising at least one cylinder with a combustion chamber, an injection valve that is provided for metering fuel, a lambda controller being provided. A start quantity adaptation value is adapted as a function of a variable that is characteristic of a rotational speed profile during a respective start of the internal combustion engine. A lambda adaptation value is adapted as a function of at least one control parameter of the lambda controller if a preset condition is met, which presupposes the existence of a quasi-stationary operating state. An intermediate correction value is adapted as a function of a change of the start quantity adaptation value since a last adaptation of the lambda adaptation value. A fuel mass to be metered is determined as a function of at least one operating variable of the internal combustion engine. The fuel mass to be metered during the start of the internal combustion engine is corrected by means of the start quantity adaptation value. The fuel mass to be metered is corrected outside of the start of the internal combustion engine as a function of the lambda adaptation value. The fuel mass to be metered is corrected as a function of the intermediate correction value until for the first time after the respective start the lambda adaptation value is adapted. In this way it is possible, particularly after the respective start up to the first adaptation of the lambda adaptation value to occur after the respective start, to realize precise control of the internal combustion engine and hence, on the one hand, keep down the production of undesirable noxious substance emissions and, on the other hand, also guarantee smooth running of the internal combustion engine. For the metering of the corrected fuel mass to be metered, in particular an actuating signal for the injection valve is generated.
In this way, knowledge of the change of the start quantity adaptation value since the last adaptation of the lambda adaptation value makes it possible to estimate the adaptation requirement for determining the fuel mass to be metered also outside of the start of the internal combustion engine, before finally a precise adaptation of the lambda adaptation value is possible by means of the at least one control parameter of the lambda controller. Thus, in this intermediate period a very precise control of the internal combustion engine may occur. In particular, after the first adaptation of the lambda adaptation value to occur after the respective start the intermediate correction value may be set to a neutral value.
According to an advantageous embodiment, the adapting of the intermediate adaptation value is carried out in such a way that a variation of the start quantity adaptation value has a relatively smaller effect upon a variation of the intermediate correction value. Thus, effects caused by a rising temperature of the internal combustion engine and in particular of its coolant as an increasing amount of time passes after the start of the internal combustion engine, as well as an overcoming of the inertia of the internal combustion engine that occurs already during the start may advantageously be taken into account and hence, after the start and before the first adaptation of the lambda adaptation value to occur after the start, a particularly precise metering of the fuel, namely particularly in respect of an air-fuel ratio to be adjusted, may be realized.
According to a further advantageous embodiment, the adapting of the intermediate correction value is carried out only if the change of the start quantity adaptation value since the last adaptation of the lambda adaptation value exceeds a predetermined threshold value. An unnecessary adaptation of the intermediate adaptation value may therefore be avoided, with a sufficiently precise correction by means of the lambda adaptation value.
According to a further advantageous embodiment, with the expiry of a preset period and/or the attainment of a preset temperature, in particular a coolant temperature, after the respective start the correcting with the intermediate correction value is returned by means of a ramp function over time to a neutral value. In this way it is possible to achieve a particularly gentle transition and hence guarantee a continuously precisely adjusted air-fuel ratio particularly well.
According to a further advantageous embodiment, the preset condition is dependent upon a rotational speed and/or a load variable. In this way, the adapting of the lambda adaptation value may be realized particularly effectively in terms of a precise determination of the corrected air-fuel mass to be metered in respect of a precisely adjusted air-fuel mixture.
In all of the figures, elements of an identical design or function are denoted by the same reference characters.